It depend on where you are in the game. Work on these ratios and fine-tune from there.

Beer: one sold every minute for every five seats
Wine: one sold every 6 minutes for every five seat
Whiskey: one sold every 10 minutes for every five seats
Cigars: something like 50% chance of selling a cigar for every whiskey sold

Note that there are conditions on these but I can't remember exactly what it was since the ratios were removed from the help file when the site was upgraded many months ago. You have something like a 2 in 5 chance of selling a whiskey every time a beer is sold. so you won't always sell whiskey or wine to these proportions but you will never sell more than these.